The present disclosure is related generally to human physiology, and more specifically to methods and apparatus for improving hemodynamic efficiency and cardiac health through enabling a user to maintain favorable coordination of repetitive musculoskeletal (MSK) movement and skeletal muscle contraction cycles with the cardiac pumping cycle.
Blood is circulated through the body by the heart during its rhythmic pumping cycle, which consists of two distinct periods—systole and diastole. Heart muscle (myocardium) contracts to eject blood from the ventricles during the systolic period of each cardiac cycle (CC), generating arterial blood pressure and flow adequate to deliver blood throughout the body, thereby transporting oxygen, nutrients, metabolic products; removing carbon dioxide and waste; and also facilitating critical physiological functions such as heat exchange. The heart subsequently relaxes during the diastolic period of the CC, when the atrial and ventricular chambers refill with blood in preparation for the heart's next contraction.
Unlike the rest of the body, which receives most of its blood flow as a result of pressure generated during systole, the heart's own arterial blood supply is delivered primarily during the diastolic portion of the cycle when the heart muscle is relaxing and the heart chambers are filling for the next contraction. Little blood flows to perfuse the myocardium during systole because the heart's contraction generates high forces within its muscular walls and thereby prevents flow through the coronary blood vessels that travel across and through the myocardium. During diastole, when the heart muscle has relaxed, residual blood pressure in the aorta drives blood flow through the coronary arteries, supplying the heart with its needed oxygen and nutrients.
In addition to the heart's pumping function, the MSK system can also play an important role in circulating blood throughout the body during physical activity. In fact, blood is rhythmically pumped via transient changes in peripheral vascular pressure induced by many types of repetitive MSK activities, including skeletal muscle contraction, skeletal muscle relaxation, and MSK movement. Examples of types of rhythmic MSK activities that can be important inducers of peripheral vascular pumping include ambulation, aerobic exercise, endurance sports, and resistance training. Rhythmic skeletal muscle contraction and relaxation can cause regular oscillations in peripheral arterial and venous pressure due to intermittent compression of the vasculature, while MSK movement leads to periodic acceleration and deceleration of the intravascular volume of blood against gravity and inertia. Regular oscillations that result from rhythmic muscle contraction can be favorably coordinated with the heart's pump cycle such that the cardiac and MSK pumps augment one another, thereby increasing blood flow and perfusion to important areas of the body with less pumping energy expended. However, unfavorable coordination of the two pumping systems can also occur, leading to decreased pumping efficiencies along with a concurrent decrease in perfusion of important tissues.
In the medical field, there are multiple therapeutic modalities that impact extra-cardiac blood flow in ways that are similar to the hemodynamic effects of the MSK system during rhythmic physical activity. These therapeutic interventions typically require large electromechanical devices in order to monitor cardiovascular rhythm and hemodynamics, while creating driving forces external to the body's own MSK system in order to impact circulation of blood throughout the body. For example, standard medical therapies such as Mechanical External Counter-Pulsation (commonly known as ECP or EECP) and Intra-aortic Balloon Counter-Pulsation (via an Intra-aortic balloon pump or IABP) are two techniques that generate periodic acceleration and deceleration of the peripheral vascular and aortic volume of blood timed in careful coordination with the heart's cycle. ECP and IABPs are well-known therapeutic modalities that have been reported in peer reviewed journal articles to be helpful in treating symptoms of myocardial ischemia, congestive heart failure, and myocardial infarction.
ECP is a noninvasive technology that rapidly mechanically compresses vasculature in the extremities in synch with the monitored cardiac rhythm in order to facilitate both coronary arterial and systemic venous blood flow to the heart during diastole. Mechanized pressure cuffs that have typically been placed around the legs, and sometimes the buttocks, are inflated in sequence, beginning with the distal limb and rapidly progressing proximally, during the diastolic period of the CC. (The upper extremities are less frequently treated due to their smaller size and lower intravascular volume.) The ECP device subsequently rapidly relaxes compression just prior to the next cardiac contraction, allowing blood to again flow through the extremities, facilitating systemic arterial blood flow from the heart during systole. ECP simultaneously pumps both arterial and venous blood from the patient's extremities in coordination with the diastolic portion of the heart cycle in order to increase the flow of oxygen-rich arterial blood to the heart musculature (myocardium), and to increase the flow of venous blood towards the hearts pumping chambers, while the heart muscle is relaxing between contractions. Furthermore, by timing the release of the cuffs' compressions just prior to the next heart contraction, with the emptied peripheral vessels reducing systemic vascular resistance (SVR), ECP improves heart function by decreasing its workload during systole. Other methods of inducing ECP for patients have been described, including rapidly and rhythmically tilting the patient, head-to-toe, in coordination with the CC, in order to induce similar cyclical increases and decreases in SVR.
Studies have suggested that powered ECP is a safe and effective non-invasive means of increasing cardiac perfusion and decreasing cardiac work, thereby decreasing angina in patients suffering from myocardial ischemia. ECP has also been used to improve cardiac function in patients suffering from Congestive Heart Failure (CHF). ECP has even been credited with improving perfusion in the treatment of cerebrovascular disease, wound management, and other disease entities where compromised vascular perfusion is present. The benefits of ECP are reported to continue beyond the duration of the therapy (common treatment of 60 minutes daily, for 4-8 weeks). The reasons cited for the long-term benefits of ECP include claims that increased shear forces in the Coronary Arteries lead to angiogenesis and increased growth of collateral coronary arteries that improve perfusion and are cardio-protective against future ischemic insult.
The combination of an increase in coronary artery perfusion pressures and flow and a decrease in cardiac afterload, also drives the beneficial cardiac effects of IABP counter-pulsation. The IABP can be utilized as a temporary cardiac assist device, as when a patient is in transient severe heart failure, when the heart requires hemodynamic support perioperatively, or in circumstances of extreme cardiovascular (CV) compromise, such as when a patient is experiencing severe angina that is refractory to standard medical therapies. The IABP device is inflated in the aorta during early diastole and deflated just prior to the onset of systole.
However, the automated mechanical pump methodologies described above require some form of apparatus that provides the pulsation supplementation. In certain cases, they require that an individual be otherwise at rest during treatment. In some cases, the methodologies require surgical or intravascular intervention.